Alloy or “special” steels are combinations of iron and
carbon with some other element, such as nickel, chromium, tungsten, vanadium,
manganese and molybdenum. All of these metals give certain distinct properties
to the steel, but in all cases the principal quality is the increase in hardness
and toughness.

Nickel steel usually contains from 3 to 3.5 percent nickel (ordinarily
not over 5 percent), and from 0.20 to 0.40 percent carbon. This steel is used
for armor plate, ammunition, bridge construction, rails, etc. One of the reasons
why nickel steel is adapted for armor plate is that it does not crack when
perforated by a projectile.

Chromium steel is well adapted for armor-piercing projectiles, owing to
its hardness, toughness and stiffness, and is extensively used for this purpose.
Chromium steel is also used in the construction of safes and for casting
subjected to unusually severe stresses, such as those used in rock-crushing
machinery, etc. The percentages of chromium used in chromium steels varies over
quite a wide range in the low-chromium and high-chromium steels.

Tungsten steel is largely employed for high speed metal cutting tools and
magnet steels. It has also been used in the manufacture of armor plate and
armor-piercing projectiles, in which case it is combined either with nickel or
chromium or with both of these metals. The property that tungsten imparts to
steel is that of hardening in the air, after heating to the required
temperature. This steel usually contains from 5 to 15 percent tungsten) although
the percentage is sometimes as high as 24 percent) and from 0.4 to 2 percent
carbon.

Vanadium steels ordinarily contain from o.16 to 0.25 percent vanadium.
The effect of vanadium is to increase the tensile strength and elastic limit,
and it gives the steel the valuable property of resisting, to an unusual degree,
repeat44d stresses. Vanadium steel is especially adapted for springs, car axles,
gears subjected to severe service, and for all parts which must withstand
constant vibration and varying stresses.

Manganese steel contains about 12 per cent manganese and from o.8 to 1.25
per cent carbon. If there is only 1.5 per cent manganese, the steel is very
brittle, and additional manganese increases this brittleness until the quantity
has reached 4 to 5.5 per cent, when the steel can be pulverized under the
hammer. With a further increase of manganese, the steel becomes ductile and very
hard, these qualities being at their highest degree when the manganese content
is 12 per cent. The ductility of the steel is brough out by sudden cooling, the
process being opposite that employed for carbon steel

Molybdenum steels have properties similar to tungsten steels, except that
a smaller quantity of molybdenum than to tungsten is required to secure similar
results.